The invention relates to a programmable controller to which a microprocessor is applied.
The latest situation is such that a process must be controlled in higher precision than ever before so as to cope with requirements for energy saving, resources saving and environmental pollution prevention. In the field of process control consequently, that of digital-control operation system to which a microprocessor is applied as disclosed in the specification of U.S. Pat. No. 4,141,065 has been developed to practice instead of a conventional analog-control operation system. The microprocessor-applied controller then has an advantage that, even though it is not referred to in the specification of U.S. Pat. No. 4,141,065, various control operations can be executed by a single hardware according to user programs, and various complementary operations can also be executed according to user programs in addition to control operations.
Now, a programmer to compose programs will be necessary before a user programmable controller is obtained. Programs are then composed generally by means of program languages like FORTRAN, BASIC, etc., therefore a considerably high extent of grammar and a tool using large computers such as compiler and generator will be necessary. Therefore, all users are not necessarily capable of composing programs freely, and there may be a case where such program as is not to be opened outside for the sake of their own know-how on control must be placed for with manufacturers. In view of the situation above, a development of such programmable controller has been desired as will enable the users to compose programs freely and also to use programs coping with a moderate system like microprocessor-applied system. The programmable controller put to practical use is constituted such that the program of the operation function required for the control operations is divided into various operation blocks, a performance number given to each of them for working as a single instruction of the user program and a given control operation is extended by combining them in the user program. For PID operation, for example, the user program is standardized for combination of PID operation block to apply a control operation to a deviation between measured value PV and set value SV, a limiter block to limit upper and lower bounds of an output of PID operation block, and a manual/automatic changeover switch to obtain an operation output MV through changing an output of the limiter block and an output of manual actuator, and also for combination of a tracking processing to change manual/automatic in balanceless and bumpless, a processing incidental to a change of internal setting and external setting, and a processing on displays of PV, SV, MV. There prepared further are PID operation block with batch and sample value PI operation block besides PID operation block, thereby constituting various programs for control operation. Thus the system wherein the function program of control operation is given in the element of various operation blocks for combination is applicable in various transforms, however, it involves a hardship that a lack of particular knowledge on control is not for the user program assembling, and a complicatedness was quite unavoidable with programs for cascade control and selective control, accordingly. Furthermore, programming was required in each occasion for control operations of a constitution, which was really troublesome.
For user programs composed according to an object of control, tests are necessary, prior to commencing control actually, to ensure that a control program conforms to specified requirements, the control program functions normally to obtain an objective control result and that an initial value of control parameter is correctly set and hardware operates normally. To carry out the tests, a control object model (hereinafter referred to as "process model") to mimic the control object is prepared in most cases and connected to the controller, which is actuated. Ths is called simulation. Simulation is taken customarily as a separate one from function of the controller, and thus a designer of the controller must prepare a suitable process model as occasion demands. To cope with the circumstances, a process simulator to approximate the process in a time lag of higher order system has been produced, however, its simple function program is not to cater for the process complicated more and more. There is a case where a complicated process model is made out and tested in software in the computer control system, however, its technique has not yet been standardized for popular use.
Furthermore, control parameters such as proportional zone P, integrating time I and differentiating time D which are used in the process control system are desirable to be nonvolatile. Since a conventional analog controller is available for setting by volume, the above requirements are satisfied. However, the situation is such that an external setting of parameters is required as seen in a remote control of parameters through communication and an adaptive control from systems of higher order, and a setting element is on the way to shift from volume to memory element. There work various kinds of writable nonvolatile memories including core, however, RAM (random access memory) ready for read/write is preferable and thus popular in respect of cost and performance in a small system like microprocessor-applied controller. However, RAM is volatile and thus involves a shortcoming that contents of the memory disappear inevitably from a device main supply coming off. A battery backup system is therefore conceivable but not perfect. If RAM volatilizes for some cause, then it cannot restart until parameters are set again.